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If the axial surface is planar, it is called an axial plane and can be described in terms of strike and dip. Folds can have a fold axis. A fold axis "is the closest approximation to a straight line that when moved parallel to itself, generates the form of the fold". [2] (Ramsay 1967).
Generally the axial plane foliation or cleavage of a fold is created during folding, and the number convention should match. For example, an F 2 fold should have an S 2 axial foliation. Deformations are numbered according to their order of formation with the letter D denoting a deformation event. For example, D 1, D 2, D 3. Folds and foliations ...
The axial surface is an imaginary plane connecting the hinge of each layer of rock stratum through the cross section of an anticline. If the axial surface is vertical and the angles on each side of the fold are equivalent, then the anticline is symmetrical. If the axial plane is tilted or offset, then the anticline is asymmetrical.
The foliations are symmetrically arranged with respect to the axial plane, depending on the composition and competency of a rock. For example, when mixed sandstone and mudstone sequences are folded during very-low to low grade metamorphism, cleavage forms parallel to the fold axial plane, particularly in the clay-rich parts of the sequence. In ...
This is related to the axis of folds, which generally form an axial-planar foliation within their axial regions. Measurement of the intersection between a fold's axial plane and a surface on the fold will provide the fold plunge. If a foliation does not match the observed plunge of a fold, it is likely associated with a different deformation event.
In his original use of the term, however, he did, in fact, use the up-dip direction of the fold. The main reason this creates confusion is a result of the common definition of fold-facing in geology, which is described as the direction (normal to the axis of a fold and corresponding to the axial plane) that points towards younger beds.
Cross-joints – Joints which are approximately perpendicular to fold axes. Diagonal joints – Joints which typically occur as conjugate joint sets that trend oblique to the fold axes. Strike joints – Joints which trend parallel to the strike of the axial plane of a fold. Cross-strike joints – Joints which cut across the axial plane of a ...
Intersection lineations are measured in relation to the two structures which intersect to form them. For instance, according to the measurement conventions of structural geology, original bedding, S 0 intersected by a fold's axial plane foliation, forms an intersection lineation L 0-1, with an azimuth and